Friction material comprising powdered phenolic resin and method of making same

ABSTRACT

The present invention relates to the process of making a non-asbestos friction material comprising a phenolic or phenolic-modified resin (and in certain embodiments, silicon nitride particles) incorporated into a fibrous base material which is then impregnated with a silicone resin. The friction material is prepared by mixing the phenolic or phenolic-modified resin (and, in certain embodiments, silicon nitride particles) into an aqueous paper formulation, forming a porous fibrous base material, impregnating the fibrous base material with a silicone resin, and heating the impregnated material to cure the phenolic resin and the silicone resin.

This is a divisional of application Ser. No. 08/114,871 filed on Aug.31, 1993, now U.S. Pat. No. 5,453,317.

TECHNICAL FIELD

The present invention relates to a method for making friction materialsand the friction materials produced thereby. In particular, thenon-asbestos friction material comprises a silicone resin impregnatedpaper which is formed from an aqueous system which includes raw paperpulp forming materials, at least one particulate phenolic resin and, incertain embodiments, silicon nitride particles and, optionally, othermaterials such as diatomaceous earth and cashew nut oil particles. It isto be understood, however, that other ingredients useful in frictionpaper formulations are compatible with the present invention. Thefriction material is useful in high energy applications and has anincreased coefficient of dynamic friction over conventional frictionmaterials.

BACKGROUND ART

New and advanced transmission systems and braking systems are beingdeveloped by the automotive industry. These new systems often involvehigh energy requirements. Therefore, the friction materials technologymust also be developed to meet the increasing energy requirements ofthese advanced systems.

The friction material must have high heat resistance in order to beuseful in the new transmission and braking systems. Not only must thefriction material remain stable at high temperatures, it must also beable to rapidly dissipate the high heat that is generated duringoperating conditions.

The high speeds generated during engagement and disengagement of the newtransmission and braking systems mean that a friction material must beable to maintain a relatively constant frictional engagement throughoutthe engagement and disengagement of the friction material. It isimportant that the frictional engagement be relatively constant over awide range of speeds and temperatures in order to minimize "grabbing" ofmaterials during braking or "shuddering" of the transmission systemduring power shift from one gear to another.

In particular, the new high energy friction material must be able towithstand high speeds wherein surface speeds are up to about 12,000feet/minute. Also, the friction material must be able to withstand highenergy pressures up to about 700 psi. It is also important that thefriction material be useful under limited lubrication conditions andalso be able to withstand the extreme pressures and speeds appliedduring use.

Previously, asbestos fibers were included in friction materials. Forexample, the Arledter et al. U.S. Pat. No. 3,270,846 patent describesphenolic and phenolic-modified resins in asbestos-filled frictionmaterials. Now, however, due to health and environmental problems,asbestos is no longer being used. However, friction materials withoutthe presence of asbestos not only encountered structural integrityproblems during processing but also lacked the thermal stability whichthe asbestos provided. More recent friction materials have attempted toovercome the absence of the asbestos in the friction material byimpregnating the paper or fiber materials with phenolic-modified andother new resins. These friction materials, however, do not rapidlydissipate the high heat generated, which may contribute to reduced heatresistance and unsatisfactory coefficient of friction performance.

While phenolic resins are conventionally used as an impregnant in wetfriction materials for wet clutch applications, the phenolic resins havevarious limitations. The phenolic resin friction materials do not havethe high heat resistance necessary for use with the new high energytransmission systems. In particular, the phenolic resins carbonize at atemperature of about 450° C. which is too low to be useful in highenergy applications. In addition, phenolic resins are rigid materialsand when the phenolic resins are used in a friction material, unevenlining wear, and separator plate "hot spots" are more likely to resultif uniform contact is not obtained.

Attempts to overcome the limitations and drawbacks of phenolic resinimpregnated friction materials include the replacement of phenolicresins with other thermosetting impregnating resins. One attempt toproduce friction materials involves the modification of a phenolic resinwith various synthesized modifications.

In order for friction materials to be useful, the friction material musthave a wide variety of acceptable characteristics. The friction materialmust be resilient (or elastic) yet resistant to compression, abrasionand stress; have high heat resistance and be able to dissipate heatquickly; and, have long lasting, stable and consistent frictionalperformance. If any of these characteristics are not present, optimumperformance of the friction material is not met.

It is also important that a suitable impregnating resin be used with thefriction material in order to achieve a high energy application frictionmaterial. The wet friction material must possess uniform absorbency andmust have good tensile and shear strengths both when saturated with thewet resin during impregnation and when saturated with brake fluid ortransmission oil during use. In selected applications, it is importantthat the friction material have a low density and high porosity suchthat there is a high fluid absorbency capacity during use. Thus, it isimportant that the friction material not only be porous, but also beflexible and compressible. The fluids absorbed into the frictionmaterial must be capable of being squeezed or released from the frictionmaterial quickly under the pressures applied during operation of thebrake or transmission. It is also important that the friction materialhave high thermal conductivity to also help rapidly dissipate the heatgenerated during operation of the brake or transmission.

In view of the need for a better friction material, and as a result ofextensive research, a new friction material with improvedcharacteristics has now been developed. As far as is known, there is nodisclosure of a friction material for use in transmission systemswherein the friction material is made by adding a powdered phenolicresin and a silicon nitride to a mixture of paper pulp, forming a paperfriction material and then impregnating the phenolic resin-paperfriction material with a silicone material.

Until the present invention there has been no disclosure or suggestionthat a powdered phenolic resin material and powdered silicon nitridecould successfully be blended with raw paper pulp to form a frictionpaper material, which could then be impregnated with a silicone materialto form a friction lining material. On the contrary, previous attemptsto use silicone resins in friction materials have not had goodacceptance in the friction lining industry. A friction lining that isimpregnated or saturated with a silicone resin has typically poor shearstrength and delamination resistance. Further, the silicone resin tendsto cause the friction lining to be too elastic which then createsundesirable friction characteristics (such as potentially large frictionfade). It is not surprising that past friction lining compositionsformed with a phenol-formaldehyde or polysiloxane resin have not beenused successfully. Such compositions do not have the necessary constantcoefficient of friction characteristics and thus fail under high energyand high heat conditions.

Accordingly, it is an object of the present invention to provide animproved friction material with reliable and improved propertiescompared to those of the prior art.

A further object of this invention is to provide friction materials Withhigh thermal conductivity, porosity and strength.

DISCLOSURE OF THE INVENTION

In order to achieve the requirements discussed above, many frictionmaterials were evaluated for friction and heat resistant characteristicsunder conditions similar to those encountered by friction materialsduring operation. Commercially available brake linings and transmissionmaterials were investigated and proved not to be suitable for use in thenew high energy applications currently being developed by the automotiveindustry.

The present invention relates to a novel non-asbestos friction materialwhich is especially useful in wet friction applications such as brakesand clutch applications where the friction material absorbs a fluid(such as brake fluid or automatic transmission fluid) during use.According to the present invention a porous fibrous base material isformed comprising a powdered phenolic or modified phenolic resin (and incertain embodiments, silicon nitride particles) homogeneously blended ormixed with an aqueous slurry of fibrous material. The porous fibrousbase material is then impregnated with a silicone based resin to form ahigh energy friction material. It is also contemplated that if thephenolic and silicone resins are solvent compatible, the phenolic resincan be blended with the silicone resin and used to impregnate orsaturate the fibrous base material. One example comprises a liquidphenolic resin in ethanol and a liquid silicone resin in isopropanol.Such high energy friction material has surprisingly high frictionstability and high heat resistance.

The friction material of the present invention comprises a resilient,heat resistant friction material. The friction material of the presentinvention prevents uneven wear or "hot spots" from developing during theuseful life of the friction material. When there is little uneven wearon the friction material, there is a more "steady state" wear on theclutch or brake and therefore, more consistent performance of the clutchor brake. Further, the friction material of the present invention showsgood shear strength such that the friction material resists delaminationduring use.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph comparing the coefficient of friction as the number ofcycles increases for various friction lining materials shown in Table IIimpregnated with the silicone T-103 resin (Examples 1, 2 and 3) andcomparative friction materials (Examples 7 and 8).

FIG. 2 is a graph comparing the coefficient of friction as the number ofcycles increases for various friction lining materials shown in Table IIimpregnated with the silicone T-40 resin (Examples 4, 5 and 6) andcomparative friction materials (Examples 7 and 8).

FIG. 3 is a graph comparing the coefficient of friction as the number ofcycles increases for various friction lining materials shown in TableIII for paper formulations (containing 5% PB206 phenolic resin in theraw paper slurry) and thereafter impregnated with a silicone T103 resin.

FIG. 4 is a graph comparing the coefficient of friction as the number ofcycles increases for various friction lining materials shown in Table IVfor paper formulations (containing a 5 % PB206 phenolic resin in the rawpaper slurry) and thereafter impregnated with a phenolic Arophene® 295resin.

FIG. 5 is a graph comparing the coefficient of friction as the number ofcycles increases for various friction lining materials shown in Table VIfor paper formulations (containing a phenolic PB206 resin powder at 0%,5% and 15% concentrations in the raw paper slurry) and thereafterimpregnated with silicone T103B resin.

FIG. 6 is a graph comparing the coefficient of friction as the number ofcycles increases for various friction lining materials shown in TableVII for various paper formulations (containing a phenolic PB206 powderresin at 0%, 5 % and 15% concentrations in the raw paper slurry) andimpregnated with a phenolic Arophene® 295 resin.

BEST MODE OF CARRYING OUT THE INVENTION

Instead of using a solvent-based phenolic resin as an impregnant, thepresent invention provides adding a solid powdered phenolic orphenolic-modified resin into an aqueous paper slurry or pulpformulation. This addition of powdered phenolic resin in the paper pulpformulation surprisingly provides the advantages of having a phenolicresin present in the friction material without the disadvantage ofhaving to remove the solvent which carried the phenolic resin. Furtheraccording to the invention, it is found that if the friction papercontaining the solid phenolic resin powder is impregnated with asilicone resin, a surprisingly good friction material results. Thefriction material has higher energy capacity and higher coefficient offriction than conventional friction materials. It is furthersurprisingly found that if silicon nitride powder is incorporated intothe aqueous paper slurry formulation along with the powdered phenolicresin, there is further improvement in the dynamic coefficient offriction characteristics of the resulting friction material. It isespecially surprisingly that powdered silicon nitride improves thefriction characteristics of the friction materials since fibers ofsilicon nitride are abrasive and thus not suitable for inclusion infriction materials due to their potential for abrasiveness of the enduse products.

Various types of fibrous or raw pulp materials are useful with thepresent invention. Particularly useful fibrous materials can becomprised of cotton fibers, glass fibers, carbon fibers and/or aramidpolymer fibers such as Kevlar® floc and/or pulp fibers which aregenerally designated as aromatic polycarbonamide materials. It is to beunderstood that various paper formulations are useful in the presentinvention and that other materials can be present in the paperformulations. For example, cotton burns at a relatively low temperatureof approximately 350° C. Therefore, a friction material has a range ofexpected thermal stability based on the raw ingredients used in thefibrous based material during the paper forming process. Fibrous basedmaterials comprise relatively high percentages of cotton would be lessthermally stable than fibrous based materials containing a morethermally stable ingredient such as graphite. The ranges and percentagesof such ingredients are dependent upon the end use of the frictionmaterial and whether such friction material is subjected to moderateenergy requirements or high energy requirements.

According to the present invention, at least one phenolic orphenolic-modified resin is incorporated into an aqueous paper pulp orslurry. Various phenolic and phenolic modified resins useful in thepresent invention include, for example, phenolic novolac resins whichare water insoluble solid particulate phenol-formaldehyde resins.

Phenolic resins useful in the present invention include the followingnovolac resins from Ashland Chemical Inc., Columbus, Ohio: PB-200A, aground novolac phenolic resin with about 3-4% free phenol; PB-200B, aground novolac phenolic resin with a hexamethylenetetramine crosslinkerand about 3-4% free phenol; PB-206, a high molecular weight powdered orground thermoplastic novolac phenolic-formaldehyde condensate resin withabout 1-2% free phenol (typically about 1% free phenol); and, PB-207, ahigh molecular weight, powdered or ground novolac phenolic-formaldehydecondensate resin with a hexamethylenetetramine crosslinker and about1-2% free phenol (typically about 1% free phenol). It is to beunderstood that various other phenolic novolac resins can be used andare contemplated as being useful with the present invention.

Both high static and high dynamic friction coefficients are required fornew friction material applications. The friction and wear performance ofthe friction material can be further improved by the incorporation ofsilicon nitride particles into the raw paper slurry during the paperformation in preferred embodiments, the silicon nitride particles havean average diameter size from about 0.5 to about 1.5 microns. In certainembodiments it has been found that silicon nitride particles having anaverage diameter size of about one micron work exceptionally well. Onetype of suitable silicon nitride particles is available from UBEIndustries Inc. as Si₃ N₄ grade SN-E-03. The silicon nitride particlesincrease the dynamic coefficient of friction When used at low levels ofabout 5%. The static coefficient of friction is increased when highlevels of silicon nitride particle concentration, at about 15%, are usedin the paper formulation.

if the initial coefficient of friction is low, then a friction materialdoes not achieve its desired constant coefficient of friction valueuntil after many uses or cycles of the friction material. The presentinvention provides a friction material having a high initial coefficientof friction. Further, when the dynamic coefficient of friction is closeto the static coefficient of friction, there is a smooth transfer fromone gear to another in a clutch operation. The present inventionachieves a surprisingly good static to dynamic coefficient of frictionratio with the addition of silicon nitride particles in the frictionpaper.

The resin used to saturate a friction material can dramaticallyinfluence the performance of the friction material. The degree oftoughness that a resin exhibits may be reflected by the frictionmaterial being able to maintain its integrity when tested. It isimportant that both the physical and frictional characteristics offriction material remain intact during the expected service period ofthe end use product such as a clutch plate or a brake lining. A frictionmaterial impregnated with a brittle resin may crack under a heavy loadwhich collapses the open structure of the friction paper matrix. On theother hand, a friction material impregnated with an elastomeric resinwould provide desired friction coefficient and torque, but may lack thewear resistance and the strength required to hold the friction papermatrix intact. Thus, an ideal resin should have high strength and stillbe flexible. A resin with high toughness would then also provide optimumfriction performance.

It is thought that the use of phenolic resin particles as an ingredientin paper formulation and the saturation of the paper formulation with asilicone resin causes a reaction with the saturating silicone resin andproduces a new species of resin as a final end product after curing. Ithas been surprisingly found that the use of a silicone resin as thesaturating resin is influential in the friction material performance.Impregnating the porous fibrous base material with the silicone resinprovides a friction material with a higher dynamic coefficient offriction than when the impregnating resin is a resole phenolic liquidresin. However, it is not intended that this invention be limited bysuch theoretical or mechanistic considerations. The point is that theprocess works, and works well, irrespective as the exact way at which itactually functions.

Silicone resins useful for saturating include, for example, thermalcuring silicone sealants and silicone rubbers. One suitable resin is theMTV silicone rubber T40 made by Wacker Silicones Corporation of Adrian,Mich. which is a one-part thermal curing system and comprises xylene andacetylacetone (2,4-pentanedione). The T40 silicone resin has a boilingpoint of about 362° F. (183° C.); vapor pressure at 68° F. mm, Hg: 21;vapor density (air-1) of 4.8; negligible solubility in water; specificgravity at 25 ° C. of about 1.09; percent volatile, by weight, 5%;evaporation rate (ether =1), less than 0.1; flash point about 149° F.(65° C.) using the Pensky-Martens method; and a viscosity, cP at 25° C.of about 900.

Another suitable silicone resin is the T-103 silicone resin, made byWacker Silicones Corp., which is a one part thermal curing system andhas a percent solids of about 50; viscosity, cps at 20° C., of about 60;specific gravity at 25° C. of 0.80; a set or gel time, minutes at 200°C., of about 1 0; a full cure time, minutes at 200° C., of about 60;and, as cured, a hardness, Shore D of about 90.

Another suitable silicone resin is the MTV silicone rubber T-107, madeby the Wacker Silicones Corp., which is a one part thermal curingsystem, having a percent solids of about 100; viscosity, cps at 25 ° C.of about 80; specific gravity at 25 ° C. of 1.00; a cure time at 150°C., of about 15 seconds, and a 200° C. of about 10 seconds. Stillanother suitable resin is the ER-84002 polydimethylsiloxane siliconeresin, made by Wacker Silicones Corp., which is a one part solid resinwhich has high reactivity and heat resistance, and has a melting rangeof about 50°-100° C., typically has a particle size of <100 microns, andis soluble in esters, alcohols and aromatic hydrocarbons. It is to beunderstood, however, that other silicone resins can be utilized with thepresent invention.

It is further contemplated that other ingredients useful in bothpreparing resin blends and in various resins used for impregnatingfibrous-based materials can be included in the friction material. Theseingredients include, for example, graphite particles, elastomeric(polymer) particles and solid cashew shell oil particles. For example,elastomeric polymer particles comprising about 70-75 % elastomericmaterial with the balance being processing aids such as product 4198from Palmer International, Worcester, Penna., is useful to provideadditional friction lining wear resistance. The rubber-type particlesallow the friction material to conform more closely to the matingseparator plate in a clutch, for example, and therefore provides anincrease in "real" versus "apparent" area of contact between theseparator plates.

Various fillers are also used in the friction material of the presentinvention. In particular, silica fillers, such as diatomaceous earth(celite), are useful. However, it is contemplated that other types offillers are suitable for use in the present invention and that thechoice of filler depends on the particular requirements of the frictionmaterial.

It is contemplated that, in certain embodiments, the fibrous basematerial can be formed from an aqueous slurry comprising about: -3-70%,by wt., aramid floc or fibers; 0-70%, by wt., cotton fibers; 5-70%, bywt., filler material; 3-80%, by wt., phenolic resin material; 3-50%, bywt., silicon nitride powder particles, 0-50%, by wt., graphite and/orcarbon particles; 0-40%, by wt., elastomeric polymer particles; 0-40%,by wt., cashew nut shell liquid particles, 0-40% by wt., silicaparticles; and 0-20% by wt., glass fibers based on the weight of theaqueous slurry formulation for the fibrous base material.

In certain embodiments the fibrous base material preferably comprisesabout: 5-35%, by wt., aramid floc or fibers: 15-55%, by wt., cottonfibers; 15-35%, by wt., filler material; 3-15%, by wt., phenolic resinmaterial; 3-10%, by wt., silicon nitride particles; 0-35%, by wt.,graphite and/or carbon particles; 2-20%, by wt., elastomeric polymerparticles; and, 2-25%, by wt., cashew nut shell liquid particles.

In certain embodiments the fibrous base material most preferablycomprises about: 3-7%, by wt., aramid floc or fibers; 40-55%, by wt.,cotton; 15-30%, by wt., filler; 5-15%, by wt., phenolic resin; 0-5%, bywt., elastomeric particles; 2-7%, by wt., cashew nut shell liquidparticles and 4-6%, by wt., silicon nitride particles.

According to the present invention, the presence of a silicone resin,when used to impregnate a fibrous base material, causes the resultingfriction material to be flexible or elastic. When pressures are appliedto the friction material of the present invention, there is a more evendistribution of pressure which, in turn, reduces the likelihood ofuneven wear. In preferred embodiments, the fibrous base material issaturated with a silicone resin at a pick up of about 45-55% resin pickup. Various methods for impregnating friction materials can be practicedwith the present invention. After the friction material has beenimpregnated with the silicone resin, the impregnated friction materialis heated. The heating cures the phenolic resin at a temperature ofabout 350° F. and cures the silicone resin at a temperature of about400° F. In addition, the heating causes the evaporation of any solvents(used to carry the impregnating silicone resin) which may be present.These solvents then can be collected and disposed of in anenvironmentally sound manner. Thereafter, the impregnated and curedfriction material is adhered to a desired substrate (such as a clutchplate or a brake shoe) by suitable means. The final density of thefriction material can be further controlled or tailored during bonding.

The following examples provide further evidence that the frictionmaterial of the present invention is an improvement over theconventional friction materials. Various preferred embodiments of theinvention are described in the following examples, which however, arenot intended to limit the scope of the invention.

EXAMPLE 1

A series of Low Velocity Friction Apparatus (LVFA) tests were performedcomparing the effectiveness of silicon nitride powder and solid cashewshell oil particles as friction particles, at high and low resinsaturation levels. All tests were run using tumbled steel separatorplates under 120 psi with Texaco TL8570 ATF as a lubricant.

EXAMPLE 1A

The dynamic coefficient of friction was increased when a level of about5 % silicon nitride powder and about 5 % solid cashew shell oilparticles are coupled with a level of about 35-40% saturating phenolicresins. While the interaction effect of both the silicon nitride powderand solid cashew shell oil particles substantially contributes to thedynamic friction coefficient, the presence of silicon nitride particlescontributes substantially more to the rise in dynamic coefficient offriction magnitude than the solid cashew shell oil particles. Thus, thesilicon nitride powder is a contributing variable in both static anddynamic friction coefficient magnitude. It was also found that thesaturating phenolic resin content in the friction material is a majorvariable influencing the increase of static friction. High concentrationof silicon nitride powder (about 15%) and saturating phenolic resin(about 48%) can increase the static friction magnitude while interactionof low silicon nitride/solid cashew shell oil particle concentration(about 5 %) and low phenolic resin concentration (about 38%) canincrease the dynamic friction magnitude.

EXAMPLE 1B

A series of Low Velocity Friction Apparatus tests were performed toevaluate types of solid resins as a friction particles. Table I belowshows a silicone resin used for saturating which increased static anddynamic coefficients of friction at all lubricant reservoir temperaturestested. The increase of dynamic friction, obtained when saturating withsilicone resin, is further increased when a low concentration ofphenolic novolac solid parties is included in the paper formulation.However, when a phenolic resin (such as Arophene 295®) is used as asaturating resin, a high concentration (about 15%) of phenolic novolacsolid particle provides no improvement in dynamic frictionalperformance.

                  TABLE I                                                         ______________________________________                                        Percent Contribution - Dynamic Friction                                                       300° F.                                                                        200° F.                                                                        100° F.                                ______________________________________                                        Silicone Resin Solid                                                                             0        0        0                                        Particles - ER84002                                                           Phenolic Novolac Solid                                                                           1        2        6                                        Particles - EP055200                                                          Type of Saturating Resin                                                                        68        82      46                                        Interaction of Phenolic                                                                         16        4       20                                        Novolac Solid Particles and                                                   Saturating Resin                                                              ______________________________________                                    

EXAMPLE 2

Friction materials saturated with silicone resins provide a highfriction coefficient and maximum thermal capacity. In order to furtherreduce lining wear, yet still maintain high friction coefficient,different types of elastomeric resins were evaluated. In particular, theWacker Silicone Corp. T-40 and T-103 silicone resin series were comparedwith several phenolic resins. In these experiments, friction materialswith 0%, 5% and 15% phenolic resin powder were made by adding thephenolic powder to the raw paper formulation. These papers weresaturated with either silicone T-103 or T-40 resins. The frictionmaterials were subjected to Full Pack tests according to moderate energyprocedure 528C. Friction and wear data was tabulated and comparisonswere made to commercially available friction materials.

    ______________________________________                                        Friction                                                                              cotton fibers/Kevlar ® fibers/celite/solid cashew                 Material                                                                              shell oil particles/Si.sub.3 N.sub.4 particles/0% PB200B                      phenolic resin powder 200 lb. basis weight/0.030 inch                         caliper                                                               Example 1                                                                             T103 resin at 42.8% P.U. (pick up)/F.L.T. (final                              lining thickness) = 0.025 inch                                        Example 4                                                                             T40 resin at 43.7% P.U./F.L.T. = 0.025 inch                           Friction                                                                              cotton fibers/Kevlar ® fibers/celite/solid cashew                 Material                                                                              shell oil particles/Si.sub.3 N.sub.4 particles/5% PB200B                      phenolic resin powder 200 lb. basis weight/0.030 inch                         caliper                                                               Example 2                                                                             T103 resin at 42.0% P.U./F.L.T.= 0.025 inch                           Example 5                                                                             T40 resin at 39.0% P.U./F.L.T. = 0.025 inch                           Friction                                                                              cotton fibers/Kevlar ® fibers/celite/solid cashew                 Material                                                                              shell oil particles/Si.sub.3 N.sub.4 particles/15% PB200B                     phenolic resin powder 200 lb. basis weight/0.030 inch                         caliper                                                               Example 3                                                                             T103 resin at 42.0% P.U./F.L.T. = 0.025 inch                          Example 6                                                                             T40 resin at 39.8% P.U./F.L.T. = 0.025 inch                           ______________________________________                                    

The addition of the phenolic powder resin into the raw paper formulationalters the combined resin formulation. The addition of phenolic powderto the friction paper pulp and saturation of the resultant frictionpaper with a silicone resin provides a friction material withperformance advantages that are not exhibited by friction materialscomprising either resin separately. In certain embodiments, the amountof phenolic powder required may vary depending on the type of siliconeresin used and also the ingredients used in the raw paper makingmaterial. For example, a larger amount of phenolic resin powder wasdesired in order to enhance the wear characteristics of assembliessaturated with the T-40 silicone resin as compared to assembliessaturated with the T-103 silicone resin.

Referring now to Table II below, the addition of a small amount ofphenolic resin powder (5%) in the paper formulation resulted in frictionand wear resistance advantages. A comparison of Examples 1 and 2 show:the dynamic friction coefficient increased from 0.163 to 0.170, a 4.3percent increase; the pack loss was reduced from 7 mils to 5 mils; and,the percent friction fade was reduced from 5.2% to 4.5%.

Final static friction readings were about 0.145-0.149 for both the 0%and 5% phenolic resin powder concentration level additions to thefriction material. At the higher 15% phenolic resin powder concentrationlevel, the static friction level is 0.137, which level is identical tothe all phenolic resin saturated comparative materials.

At the percentages higher than about 15% phenolic resin powder additionto the raw material, the friction materials showed adverse performancetraits that began to approach the same performance as from an allphenolic system. FIG. 1 is a graph showing the high speed frictionversus cycles for the samples described in Table II comprising in theT103 saturated material and comparative production materials.

Surface appearance rankings of the friction materials improved: theabrasion ranking was reduced from "2" to "0," and the glazing rankingreduced from "3" to "1" on a scale of one to five where the lowernumbers reflect a better or preferred ranking. The combined effect ofall these performance improvements clearly indicates an advantage ofadding a phenolic powder to the raw paper formulation.

When the T40 silicone resin was used as the saturating resin, a higherpercent of phenolic powder in the raw paper formulation may be useful inorder to achieve optimum performance advantages. At 15 % phenolic resinpowder concentration, the percent friction fade is reduced to 3.9%,compared to 10.2% and 13.2% at lower concentrations. The more elasticcharacter of the T40 silicone resin as compared to the T103 siliconeresin contributes to the fact that about 15% phenolic resin powder inthe paper formulation provides a friction material with the optimumresults. The final dynamic friction coefficient is 0.170 for the sampleswith 15 % phenolic resin concentration. Friction and wear values areimproved when phenolic resin powder is added to the raw paperformulation.

The lining surface condition rankings are excellent at the 15% phenolicresin powder concentration level. Glazing is a low "1" ranking.Abrasion, breakout, and delamination are all ranked "0." These are thesame rankings as the samples saturated with the T 103 silicone resin atthe 5% phenolic resin powder concentration level.

The static friction coefficient for both the T40 and T103 siliconesaturated materials are similar at about 0.149. In all tests, thecomparative examples 7 and 8 had lower static friction coefficientscompared to the silicone resin saturated friction materials. FIG. 2 is agraph showing the high speed friction versus cycles for the T40saturated material and the comparative production materials. Averagefriction coefficients are plotted against the number of cycles for alltests.

Material containing phenolic resin and saturated with silicone T103 andT40 resins performed with higher static (about 8 to about 9%) anddynamic (about 20 to about 24%) friction coefficients compared to thecomparative production materials.

The pack loss data shows that the friction materials saturated with T103resin exhibited about half the amount of wear as the comparativeproduction material.

The addition of phenolic powder into the fibrous base materialformulation and saturation with silicone resin provides an increase ofdynamic friction coefficient, improved resistance to high speed dynamicfriction fade, improved resistance to surface damage, and improvedassembly wear resistance.

                                      TABLE II                                    __________________________________________________________________________    Full Pack Test Laboratory Friction Data                                       Procedure 528C/Exxon 1975 Type "H" ATF - 200° F.                       Phenolic Resin Powder PB200B/1050 Cycle Data                                              Low Speed                                                                            High Speed                                                                          Pack Loss                                                                           Percent                                                                            Assembly                                  Material Identification                                                                   Dynamic (a)                                                                          Dynamic                                                                             Mils  Fade (b)                                                                           Rank (c)                                  __________________________________________________________________________    Sample 1: 0% Phenolic                                                                     0.145  0.163  7    5.2  2, 0, 3, 0                                T103 Silicone Resin                                                           Sample 2: 5% Phenolic                                                                     0.149  0.170  5    4.5  0, 0, 1, 0                                T103 Silicone Resin                                                           Sample 3: 15% Phenolic                                                                    0.137  0.154 10    7.8  1, 0, 2, 0                                T103 Silicone Resin                                                           Sample 4: 0% Phenolic                                                                     0.149  0.167 14    10.2 1, 0, 2, 0                                T40 Silicone Resin                                                            Sample 5: 5% Phenolic                                                                     0.149  0.165 17    13.2 1, 0, 1, 0                                T40 Silicone Resin                                                            Sample 6: 15% Phenolic                                                                    0.149  0.170 13    3.9  0, 0, 1, 0                                T40 Silicone Resin                                                            Comparative Sample 7                                                                      0.129  0.137 20    8.1  2, 1, 2, 0                                Comparative Sample 8                                                                      0.138  0.136 14    8.7  1, 1, 2, 0                                __________________________________________________________________________     (a) Low speed dynamic friction coefficient.                                   (b) Percent high speed dynamic friction fade between cycles 200 and 1050.     (c) Assembly rank values given are abrasion, breakout, glazing, and           delamination, respectively.                                              

EXAMPLE 3

Referring now to Table Ill below, a comparison was made between phenolicresin alone, and with silicon nitride particles as ingredients in anaqueous paper formulation. The final resulting resin mixture comprisedabout 5% PB206 phenolic resin powder. Five different raw paperformulations were made: XP116, XP1 21,941 6, RHS30, and HS95.

    ______________________________________                                        XP116: cotton fibers/Kevlar ® fibers/celite/graphite                             particles/carbon particles/PB206 phenolic resin                        XP121: cotton fibers/Kevlar ® fibers/celite/graphite                             particles/PB206 phenolic resin                                         9416:  cotton fibers/Kevlar ® fibers/celite/solid cashew                         shell oil particles/elastomeric (polymer) particles/                          Si.sub.3 N.sub.4 particles/PB206 phenolic resin                        RHS-30:                                                                              Kevlar ® fibers/celite/silica particles/elastomeric                       (polymer) particles/glass fibers/PB206 phenolic resin                  HS95:  cotton fibers/Kevlar ® fibers/celite/solid cashew                         shell oil particles/Si.sub.3 N.sub.4 particles/PB206 phenolic          ______________________________________                                               resin                                                              

The data in Tables III and IV below support the synergistic effectbetween powdered phenolic resin in the fibrous base material and thesilicone resin. This data effectively illustrates the performance ofhaving the two resins present in an end product. The same type offavorable synergistic effect Was not shown when a phenolic powder and aphenolic saturating resin were used.

EXAMPLE 3A

The hand sheet formulations above were saturated with liquid siliconeresin to achieve about a 50-55% silicone resin pick up, and then curedfor 120 minutes at 400° F. to form friction materials. All the frictionmaterials were made at 200 lb. basis weight and were bonded, wire sideup, to form an assembly part. The friction materials were submitted forclutch pack tests according to procedures 528 and 527. All tests wereperformed with Exxon 1975 Type "H" lubrication. The results are shown inTable II below.

Most of the friction materials resulted in a pack gain after testing.All the materials tested had surface appearance rankings of "0" or "1."The materials saturated with the T103 silicone resin had S/D ratiosranging from 0.95 to 1.25. The average friction versus cycle graphs forthe individual materials listed in Table II are shown in FIG. 3.

Friction materials comprised of the HS121 (6-1187) and 9416 (6-1190)type materials both produced a dynamic friction coefficient of 0.160after an about 6% and 10% fade, respectively.

The XP116 type material saturated With silicone T103B (6-1189) producedthe lowest dynamic friction coefficient of 0.105 after a 19% fade. Thismaterial tested with an ascending curve (1.25 S/D ratio).

RHS30 type material (6-1188) resulted in 0.142 dynamic frictioncoefficient after a 13% fade. HS95 type material (6-1177) failed thetest after 550 cycles.

                                      TABLE III                                   __________________________________________________________________________    Full Pack Laboratory Data - 1050 Cycle                                        Exxon 1975 Type "H" ATF - Procedure 528                                       Silicone T103 Saturated Resin System - 5% PB206 in raw paper slurry           Wire Side Up - Final Lining Thickness = 0.020"                                Material                                                                             Fric.                                                                              Fric. Fric.                                                                              Pack Loss                                                                           Percent                                                                            Assembly                                    Formulation                                                                          ui (a)                                                                             ud (b)                                                                              us (c)                                                                             (mils)                                                                              Fade (d)                                                                           Rank (e)                                    __________________________________________________________________________    XP116  0.105                                                                              0.121 0.131                                                                               0.0  19.2 0, 0, 1, 0                                  Test 6-1189                                                                   XP121  0.160                                                                              0.157 0.152                                                                              -9.6   5.9 0, 0, 1, 0                                  Test 6-1187            (gain)                                                 RHS30  0.142                                                                              0.139 0.138                                                                              -4.3  13.4 0, 0, 1, 0                                  Test 6-1188            (gain)                                                 HS95   0.138                                                                              0.140 0.137                                                                               5.0  NA   NA                                          Test 6-1177                                                                          (@ 550)*                                                                           (@ 500)*                                                                            (@ 550)*                                                                           (@ 550)*                                               9416   0.158                                                                              0.158 0.162                                                                              -1.6   9.7 0, 1, 1, 0                                  Test 6-1190            (gain)                                                 __________________________________________________________________________     (a) Fric. ui is the dynamic friction coefficient at high speed.               (b) Fric. ud is the midpoint friction coefficient.                            (c) Fric. us is the slow speed friction coefficient.                          (d) Percent friction fade (using ui) is calculated between cycles 200         through 1050.                                                                 (e) Assembly rank values given are abrasion, breakout, glazing, and           delamination, respectively.                                                   * Indicates the test stopped, or failed, at the cycle number given.      

EXAMPLE 3B

Referring to Table IV below, samples of the above paper formulationswere saturated with phenolic Arophene® 295 resin. Except for the 9416paper formulation, all the friction materials saturated with Arophene®295 phenolic resin failed the test. The 9416 type material (test 6-1182)had a 0.115 dynamic friction coefficient after 15% fade. This testresulted in an unfavorable ascending (S/D ratio) curve, but the surfaceappearance rankings were favorable. Only the glaze ranking of "3" washigh. Table IV below lists a summary of friction and wear data. FIG. 4illustrates the combined friction versus cycles for the phenolicArophene® 295 saturated materials.

EXAMPLE 3C

After the ingredients are mixed to form the fibrous base material, theingredients are placed on a screen and water is removed using gravityand vacuum. The wire side of the fibrous base material tends to reflecta topography similar to that of the screen used. Also, depending uponthe individual ingredients, densities and rate of water extraction, thesmaller and lighter weight particles may tend to accumulate towards thescreen side slightly more than towards the felt side of the fibrous basematerial. The felt side of the fibrous base material may tend to have atopography which is closer to that produced from the flowing waterslurry. Typically, the wire side of the friction material will have aslight symmetrically-type pattern apparent while the felt side reflectsa more random water flow or possibly swirled-type pattern.

The material surface profiles of the above formulations were comparedfor both "wire" and "felt" sides of the assembly. A summary of thesurface texture results is given in Table V below. It is seen in TableIll above that the XP116 and XP121 materials saturated with a siliconeresin successfully completed the Full Pack test; yet these samematerials failed when saturated with a phenolic resin within 750 and 300cycles, respectively. This wire side failure of phenolic materials showsthe relationship between surface topography and clutch performance. The9416 material was roughest in terms of its arithmetic average (Ra). Theingredients used in the formulation influence the resulting topographyof the friction material. The wire side of friction material tends to berougher than the felt side.

                                      TABLE IV                                    __________________________________________________________________________    Full Pack Laboratory Data - 1050 Cycle                                        Exxon 1975 Type "H" ATF - Procedure 528                                       Silicone 295 Saturated Resin System - 5% PB206 in raw paper slurry            Wire Side Up - Final Lining Thickness = 0.020"                                Material                                                                             Fric.                                                                              Fric. Fric.                                                                              Pack Loss                                                                           Percent                                                                            Assembly                                    Formulation                                                                          ui (a)                                                                             ud (b)                                                                              us (c)                                                                             (mils)                                                                              Fade (d)                                                                           Rank (e)                                    __________________________________________________________________________    XP116  0.118                                                                              0.130 0.129                                                                              NA    NA   NA                                          Test 6-1181                                                                          (@ 750)*                                                                           (@ 750)*                                                                            (@ 750)*                                                    XP121  0.124                                                                              0.136 0.135                                                                              NA    NA   NA                                          Test 6-1179                                                                          (@ 300)*                                                                           (@ 300)*                                                                            (@ 250)*                                                    RHS30  0.128                                                                              0.160 NA   NA    NA   NA                                          Test 6-1180                                                                          (@ 100)*                                                                           (@ 100)*                                                          HS95   0.144                                                                              0.164 0.158                                                                              NA    NA   NA                                          Test 6-1178                                                                          (@ 150)*                                                                           (@ 150)*                                                                            (@ 150)*                                                    9416   0.115                                                                              0.128 0.139                                                                              3.8   14.8 0, 1, 3, 0                                  Test 6-1182                                                                   __________________________________________________________________________     (a) Fric. ui is the dynamic friction coefficient at high speed.               (b) Fric. ud is the midpoint friction coefficient.                            (c) Fric. us is the slow speed friction coefficient.                          (d) Percent friction fade (using ui) is calculated between cycles 200         through 1050.                                                                 (e) Assembly rank values given are abrasion, breakout, glazing, and           delamination, respectively.                                                   * Indicates the test stopped, or failed, at the cycle number given.      

                                      TABLE V                                     __________________________________________________________________________    Surface Texture Parameters - Talysurf 10                                      Mean data - Five profiles per assembly side                                           Sm      Ra       Rp       Rv        Rt        HTP*                    __________________________________________________________________________    XP116 wire                                                                            4.3 +/- 1.0                                                                           208.4 +/- 25.8                                                                         667.3 +/- 63.3                                                                         892.1 +/- 65.1                                                                          1559.4 +/- 113.2                                                                        237.2 +/- 36.06         XP116 felt                                                                            4.7 +/- 0.6                                                                           191.9 +/- 20.3                                                                         633.2 +/- 74.9                                                                         972.1 +/- 118.9                                                                         1605.3 +/- 187.7                                                                        226.2 +/- 29.05         XP121 wire                                                                            3.9 +/- 0.4                                                                           207.3 +/- 23.7                                                                         708.5 +/- 137.6                                                                        1056.6 +/- 223.1                                                                        1765.1 +/- 300.1                                                                        246.9 +/- 52.77         XP121 felt                                                                            5.0 +/- 1.0                                                                           206.8 +/- 24.0                                                                         777.5 +/- 141.6                                                                        871.8 +/- 148.7                                                                         1649.3 +/- 225.9                                                                        252.4 +/- 21.57         RHS30 wire                                                                            3.8 +/- 0.6                                                                           139.6 +/- 17.7                                                                         459.8 +/- 153.2                                                                        613.9 +/- 102.7                                                                         1073.7 +/- 252.6                                                                        173.2 + /- 36.41        RHS30 felt                                                                            3.7 +/- 0.5                                                                           159.9 +/- 38.4                                                                         580.7 +/- 204.9                                                                        662.6 +/- 160.4                                                                         1243.3 +/- 325.7                                                                        231.2 +/- 83.64         HS95 wire                                                                             4.1 +/- 0.8                                                                           204.5 +/- 27.2                                                                         838.8 +/- 291.1                                                                        980.7 +/- 226.4                                                                         1819.5 +/- 449.4                                                                        268.1 +/- 98.15         HS95 felt                                                                             4.1 +/- 0.7                                                                           177.8 +/- 15.3                                                                         564.3 +/- 42.0                                                                         790.2 +/- 146.1                                                                         1354.4 +/- 167.0                                                                        198.6 +/- 20.02         9416 wire                                                                             6.3 +/- 1.2                                                                           277.8 +/- 24.1                                                                         917.8 +/- 217.8                                                                        1225.4 +/- 175.9                                                                        2143.2 +/- 337.4                                                                        400.1 +/- 88.38         9416 felt                                                                             4.9 +/- 0.3                                                                           251.0 +/- 26.6                                                                         938.4 +/- 234.7                                                                        1064.9 +/- 408.6                                                                        2003.3 +/- 611.2                                                                        352.3                   __________________________________________________________________________                                                          +/- 76.57                *HTP from 5%-30%                                                              Ra = arithmetic mean of the departures of the roughness profile from the      mean line.                                                                    Rp = the maximum height of the profile above the mean line within the         assessment length.                                                            Rv = the maximum depth of the profile below the mean line within the          assessment length.                                                            Rt = Rp + Rv                                                                  Sm = the mean spacing between profile peaks at the mean line, measured        over the assessment length.                                                   HTP = material bearing ratio                                             

EXAMPLE 4

Friction materials were made from the 9416 paper formulation containingPB206 phenolic resin powder at 0%, 5%, and 15% concentration levels, andthen saturated with silicone resins.

EXAMPLE 4A

When the friction materials containing 5% powder were saturated with asilicone resin, the pack wear was lowest, and friction the highest. Thefriction initial and midpoint friction slightly increased from 0.152 to0.158, as shown in Table VI below in tests 6-1186 and 6-1190. Wearresistance for the 5 % phenolic resin was improved from minus 3.0 mils(test 6-1186) to zero (test 6-1190). However, when the higher 15 %concentration of phenolic resin powder (test 6-1191) was used, thematerial failed the test within 750 cycles.

Saturating the fibrous base material with a different type of siliconeresin (for example, as shown in T40 silicone (Test 6-1154) versus T103silicone (Test 6-1186)) produces friction materials that have differentfriction and wear results (as shown in Table VI below). The frictionmaterials saturated with the T40 silicone resin had higher frictioncoefficient, and higher wear resistance. However, the surface appearanceof these T40 silicone saturated friction materials exhibitedsubstantially more abrasion compared to the same material saturated withthe T103 silicone saturated friction materials.

FIG. 5 illustrates the friction performance improvement obtained fromthe addition of phenolic resin powder to the paper formulation for thefibrous base materials saturated with T103 silicone resin (Tests 6-1186,6-1190 and 6-1191) described in Table VI.

                                      TABLE VI                                    __________________________________________________________________________    Full Pack Laboratory Data                                                     Exxon 1975 Type "H" ATF - Procedure 528                                       Silicone T103 Saturated Resin System - 9416 Type Material                     Wire Side Up - Final Lining Thickness = 0.020"                                Phenolic PB206 Powder @ 0% 5% and 15% Concentration in Raw Paper Slurry       Material                                                                             Fric.                                                                              Fric. Fric.                                                                              Pack Loss                                                                           Percent                                                                            Assembly                                    Formulation                                                                          ui (a)                                                                             ud (b)                                                                              us (c)                                                                             (mils)                                                                              Fade (d)                                                                           Rank (e)                                    __________________________________________________________________________    0% PB206                                                                             0.152                                                                              0.152 0.148                                                                               3.0  10.6 0, 2, 2, 0                                  Test 6-1186                                                                   5% PB206                                                                             0.158                                                                              0.158 0.162                                                                              -1.6  9.7  0, 1, 1, 0                                  Test 6-1190            (gain)                                                 15% PB206                                                                            0.156                                                                              0.163 0.145                                                                              NA    NA   NA                                          Test 6-1191                                                                          (@ 800)*                                                                           (@ 800)*                                                                            (@ 750)*                                                    0% PB206                                                                             0.166                                                                              0.166 0.166                                                                              -3.0  7.3  3, 2, 2, 0                                  Test 6-1154            (gain)                                                 T40 Resin                                                                     __________________________________________________________________________     (a) Fric. ui is the dynamic friction coefficient at high speed.               (b) Fric. ud is the midpoint friction coefficient.                            (c) Fric. us is the slow speed friction coefficient.                          (d) Percent friction fade (using ui) is calculated between cycles 200         through 1050.                                                                 (e) Assembly rank values given are abrasion, breakout, glazing, and           delamination, respectively.                                                   * Indicates the test stopped, or failed, at the cycle number given.      

EXAMPLE 4B

In order to determine whether there was any performance advantage fromthe addition of the phenolic resin powder to a material saturated withphenolic resin, three additional tests were performed. Frictionmaterials of the 9416 formulation were made with 0%, 5%, and 15 %concentrations of phenolic resin powder and then saturated with aphenolic Arophene® 295 resin. As seen in Table VII below, there is noadvantage to adding a phenolic resin powder addition to a fibrous basematerial that will be saturated with a phenolic resin. The higher amountof phenolic resin to the fibrous base material resulted in slightlylower dynamic friction coefficient, and less wear resistance. Thefriction dropped from 0.113 to 0.097 with the addition of 15 % phenolicresin powder. Pack loss also increased from roughly zero to nearly 9mils with the powder addition.

FIG. 6 illustrates the friction performance for friction materialscontaining different amounts of phenolic resin powder in the fibrousbase formulation and saturated with a phenolic resin.

                                      TABLE VII                                   __________________________________________________________________________    Full Pack Laboratory Data                                                     Exxon 1975 Type "H" ATF - Procedure 528                                       Phenolic Arophene ® 295 Saturated Resin System - 9416 Type Material       Wire Side Up - Final Lining Thickness = 0.020"                                Phenolic PB206 Powder @ 0% 5% and 15% Concentration in Raw Paper Slurry       Material                                                                             Fric.                                                                              Fric.                                                                              Fric.                                                                              Pack Loss                                                                           Percent                                                                            Assembly                                     Formulation                                                                          ui (a)                                                                             ud (b)                                                                             us (c)                                                                             (mils)                                                                              Fade (d)                                                                           Rank (e)                                     __________________________________________________________________________    0% Phenolic                                                                          0.113                                                                              0.132                                                                              0.146                                                                              -1.1  17.5 0, 1, 4, 0                                   Test 6-1185           (gain)                                                  5% Phenolic                                                                          0.115                                                                              0.128                                                                              0.139                                                                              3.8   14.8 0, 1, 3, 0                                   Test 6-1182                                                                   15% Phenolic                                                                         0.097                                                                              0.117                                                                              0.141                                                                              8.6   23.0 0, 1, 4, 0                                   Test 6-1184                                                                   __________________________________________________________________________     (a) Fric. ui is the dynamic friction coefficient at high speed.               (b) Fric. ud is the midpoint friction coefficient.                            (c) Fric. us is the slow speed friction coefficient.                          (d) Percent friction fade (using ui) is calculated between cycles 200         through 1050.                                                                 (e) Assembly rank values given are abrasion, breakout, glazing, and           delamination, respectively.                                              

INDUSTRIAL APPLICABILITY

The present invention is useful as a high energy friction material foruse with clutch plates, transmission bands, brake shoes, synchronizerrings, friction disks or system plates.

The above descriptions of the preferred and alternative embodiments ofthe present invention are intended to be illustrative and are notintended to be limiting upon the scope and content of the followingclaims.

I claim:
 1. A process for producing a non-asbestos friction materialcomprising adding at least one phenolic or phenolic-modified resin to anaqueous slurry comprising fibrous material and at least one fillermaterial, forming a porous fibrous base material from the aqueousslurry, impregnating the porous fibrous base material with a siliconeresin, and thereafter heating the impregnated fibrous base material tocure the phenolic or phenolic-modified resin and the silicone resin. 2.The process of claim 1, wherein the phenolic resin is a phenolic novolacresin and the amount of phenolic novolac resin present ranges from about3% to about 80%, by weight, based on the weight of the fibrous basematerial.
 3. The process of claim 2, wherein silicon nitride particlesare added to the aqueous slurry, the amount of silicon nitride particlespresent ranging from about 3% to about 50%, by weight, of the fibrousbase material.
 4. A process for forming a non-asbestos friction materialcomprising forming a porous fibrous base material and impregnating theporous fibrous base material with a resin, the improvement comprisingwherein the porous fibrous base material is formed by incorporating apredetermined amount of at least one powdered phenolic orphenolic-modified resin and a predetermined amount of silicon nitrideparticles therein, and impregnating the porous fibrous base materialwith a silicone resin wherein the silicone resin provides the frictionmaterial with a higher dynamic coefficient of friction than when theimpregnating resin is a resole phenolic liquid resin, and wherein theincorporation of the phenolic powder resin in the porous fibrous basematerial improves wear resistance of the friction material.
 5. Theprocess of claim 4, wherein the ratio of the static coefficient offriction to the dynamic coefficient of friction is lower than if asilicone resin is not used as an impregnant and a resole phenolic resinis used as an impregnant.